Recirculating heat treating furnace



Dec. 29, 1964 H. N. IPSEN RECIRCULATING HEAT TREATING FURNACE 5 Sheets-Sheet 2 Filed Feb. 5. 1960 Dec. 29, 1964 H. N. IPSEN RECIRCULATING HEAT TREATING FURNACE S Sheets-Sheet 3 Filed Feb. 5, 1960 United States Patent 3,163,6514 RECIRCULATENG HEAT TREATING FURNAQE Harold N. lpsen, 715 S. Main St, Rockford, Ill.

rhesus). 5, race, $65K. No. 6,910 3 Qiairns. or. ass- This invention relates to a furnace in which workpieces are treated bycirculating the heated atmosphere within the furnace about the work and, more particularly, to a furnace in which the atmosphere is circulated by a fan and is heated by the productsv of combustion of a burning gas which is delivered from a burner to the fan. I

The general object of the invention is to providein a furnace of the above character a novel arrangement for introducing the burning gas into the furnaceso that the temperature of the work maybe controlled with great accuracy and, more specifically, so that there is no thermal head to cause overheating of the work and there are nohot spots.

A more detailed object is to introduce the burning gas through a comparatively thin-wallecl tube which is placed prevent the overheating of the tube, the relatively low mass of the tube preventing the existence of any appreciable thermal head.

In a more detailed aspect, another object is to project the burner tube through the bottom wall of the furnace and across the path of the atmosphere leaving the fan so that the tip and, all the connections are beneath the furnace and the tube, even though his bent and impinged by burning gases, is kept below a red heat.

Other objects and advantages of the invention will becomes apparent from the following detailed description taken in connection with the accompanying drawings, in which FIGURE 1 is a longitudinal sectional View of a heat treating furnace embodying the novel features of the present invention.

FIG. 2 is a fragmentary perspective view of the parts surrounding the fan. 1 v

FIG. 3 is a sectional view taken along the line 3-3 in FIGURE 1.

FIG. 4 is a fragmentary sectional view taken along the line 44 in FIGURE 3. 7

FIG. 5 is a longitudinal sectional view of a heat treating furnace employing a modified revision of the lHVElK'. tion.

FIG. 6 is a sectional view taken along the lines 6-6 in FIG. 5.

For purposes of illustration, the invention as shown in FIGS. 1 through 4 is embodied in a furnace 19 for heat treating metal workpieces which may conveniently be carriedin a tray or basketlll. The latter is supported within the furnace chamber 12 on a horizontal platform 13 which is spaced above the floor 14 of the charm her and is composed of a plurality of rollers 15. Doorcontrolled openings 16 in the end walls 17 of the furnace permit the trays to be loaded into the furnace chamber.

To treat the workpieces, heated atmosphere, which preferably is a non-oxidizing gas, is circulated bya fan 18 through a horizontal duct 19 and above and below the platform 13. The duct 19 is defined by the floor 14 and a horizontal partition 20 which is spaced above the floor and is formed with adjustable slots or holes 21st one end portion of the duct to permit the atmosphere to' leave the duct and circulate about the work.

i Herein, the fan 18 is' of the centrifugal impeller type thereof opposite the holes 21. A motor 26 secured to the underside of the wall 25 drives the shaft to cause the vanes 22 to discharge atmosphere laterally through an outlet 27 in a casing 28 which surrounds the impeller- 13 in the path of circulation of the furnace atmosphere to p and is secured by brackets 29 to angle bars 3% on the furnace Walls. As indicated by the arrows in FIGURE 1, the atmosphere flows along the duct 19, up through the holes 21, above and below the platform 13 and axially back to the impeller. A screen 31 is disposed over the impeller to prevent articles from dropping into the vanes 22 and is secured to a conical ring 32 which rests on the casing 28 and, through the medium of a bracket 33, is secured to an angle bar 34 on the front furnace wall.

In order to heat the atmosphere as it is circulated by the impeller 1%, hot gases are delivered to the intake of the impeller and are mixed with the cooler atmosphere. For this purpose, a suitable combustible gas is delivered through a supply pipe 35 to a burner tip 36 from which the burning gases are directed to the intake of the impeller.

In accordance with the present invention, the burning gases are delivered from the tip 36 to the impeller 13 by a tube 37 which is constructed and arranged in a novel manner so as to provide uniform and accurate heating of the work by eliminating the presence of hot spots and thermal heads which could cause overheating of the work. To these ends, the tube 37 is comparatively thinwalled so as to be lowin mass and thereby incapable of storing an appreciable amount of heat. Moreover, the tube'is placed in the path of circulation of the furnace atmosphere which cools the tube and prevents any portion of the tube from attaining a red heat.

' In the form of the invention shown in FIGS. 1 through 4, tube 37 and the associated parts are further arranged in a novel manner so as not to add to the overall dimensions of the furnace 1 0 while still producing a comparatively long tube life and a uniform heating of the workpieces. This is achieved by bending the tube 37 and by utilizing the atmosphere leaving the, impeller 13 for cooling the tube and preventing the latter from being overheated.

As shown in FIGS. 1 through 4 of the drawings, the tube 3'7,"which may be made of stainless steel, enters the interior of the furnace 10 through the bottom wall 25 and has a straightvertical section 38 which crosses the duct 19 in front of the outlet 27 of the impeller casing 28. At the top of this section, the tube is bent laterally to provide a horizontal section 39 which projects through the screensupporting ring 32 and in over the impeller 18. The section 39 terminates over the shaft 23, that is, over the intake of the impeller, and this end of the tube is cut off at an angle to form a downwardly directed opening for the heated gases fiowingthrough the tube. The other end 1 of the tube is disposed beneath the furnace and the burner tip 36 is secured to this end so that, as a result, all of the parts of the burner'assembly are within the confines of the furnace proper.

With the foregoing arrangement, the combustible gas supplied through the pipe 35 is ignited at the tip 36. The burning gases are drawn through the tube 37 by the suc tion of the impeller 18 and, as these gases leave the tube, they mix with the atmosphere which has just passed over the work and is returning to the impeller 18. Thus, the gases entering the intake of the impeller are heated for recirculation.

The invention may take the form shown in FIGS. 5

' and 6 in which the corresponding parts are identified by the same but primed reference characters. In this case,

the impeller 18 is disposed on the horizontal shaft 23' greases Wardly and into the horizontal passage 19 at the bottom of the furnace chamber 12. From the passage, the atmosphere is directed upwardly by deflectors 4' and flows through the platform 13', across the work in the tray 11' and horizontally back to the intake of the impeller through a bafile 42 and a tapered shell 43.

In the modified form of the invention, the tube 37 is straight and projects up through the bottom wall 25 of the furnace. The tube is disposed between the impeller 13' and the baffle 42 and terminates at the axis of the impeller with the upper end of the tube being cut at an angle to provide a lateral outlet opening toward the impeller. The burner tip 36 projects into the lower end of the tube and is secured to the bottom wall 25'.

It will be observed that, in each instance, the tube 37 or 37 is in the path of circulation of the furnace atmosphere and is cooled thereby. Such cooling permits the use of a comparatively thin-walled tube which has a low mass. As a result, the tube is incapable of storing an appreciable amount of heat and there is almost no heating of the work due to stored heat in thetube. This makes it possible to control the temperature Within the furnace chamber with much greater accuracy than with prior arrangements. Also contributing to the accuracy is the fact the cooling effect of the furnace atmosphere prevents hot spots on the tube, even if the latter is bent as at 40 in FIGS. 1 through 4, and thus there is no uneven heating of the work.

This application is a continuation-impart of my copending application Serial No. 696,720, filed November 15, 1957 and now abandoned.

I claim as my invention:

1. In a heat treating apparatus, the combination of, a furnace having a heating chamber defined by top, bottom, side and end Walls, an impeller disposed within said chamber and comprising a shaft and a plurality of vanes angularly spaced around and radiating from the shaft,

iechanisrn operable to turn said impeller thereby to circulate the atmosphere within said chamber, means in said chamber defining a predetermined path of circulation for said atmosphere, a thin-walled tube projecting through one of said walls and into said chamber and terminating in an outlet adjacent the axis of said impeller, substantially the entire portion of the tube within said chamber extending transversely across said path, a burner tip disposed adjacent said one wall and coaxial with said tube,

' and means for supplying a combustible gas to and burning the same at said tip thereby to burn the gas along the length of the tube portion in said chamber and deliver hot gases to the axis of said impeller, said tube extending across said path to be cooled by the atmosphere circulating within said chamber.

2. In a heat treating apparatus, the combination of, a furnace having a heating chamber defined by top, bottom, side and end walls, an impeller disposed near said bottom wall and comprising a vertical shaft and a plurality of vanes angularly spaced around and radiating from the shaft, means operable to turn said impeller thereby to circulate the atmosphere within said chamber, a casing for said impeller having an outlet to direct the atmosphere leaving the impeller horizontally along said bottom wall, a thin-Walled tube having a vertical portion projecting through said bottom wall and disposed in front of said outlet, the upper end portion of said tube being bent laterally to project over said impeller and having an outlet above the axis of the impeller, and means for supplying and burning a gas at the lower end of said tube whereby hot gases are delivered through the tube to the axis of said impeller, said tube being cooled by the atmosphere leaving said impeller.

3. Heat treating apparatus as defined in claim 1 in which the shaft of said impeller is horizontal and said tube is straight and extends vertically through said bottom wall.

References Cited in the file of this patent UNITED STATES PATENTS 1,906,799 Lobley May 2, 1933 2,182,218 Woodson Dec. 5, 1939 2,233,474 Dreffein Mar. 4, 1941 2,479,102 Dailey Aug. 16, 1949 FOREIGN PATENTS 571,423 Great Britain Aug. 23, 1945 

1. IN A HEAT TREATING APPARATUS, THE COMBINATION OF, A FURNACE HAVING A HEATING CHAMBER DEFINED BY TOP, BOTTOM, SIDE AND WALLS, AND IMPELLER DISPOSED WITHIN SAID CHAMBER AND COMPRISING A SHAFT AND A PLURALITY OF VANES ANGULARLY SPACED AROUND AND RADIATING FROM THE SHAFT, MECHANISM OPERABLE TO TURN SAID IMPELLER THEREBY TO CIRCULATE THE ATMOSPHERE WITHIN SAID CHAMBER, MEANS IN SAID CHAMBER DEFINING A PREDETERMINED PATH OF CIRCULATION FOR SAID ATMOSPHERE, A THIN-WALLED TUBE PROJECTING THROUGH ONE OF SAID WALLS AND INTO SAID CHAMBER AND TERMINATING IN AN OUTLET ADJACENT THE AXIS OF SAID IMPELLER, SUBSTANTIALLY THE ENTIRE PORTION OF THE TUBE WITHIN SAID CHAMBER EXTENDING TRANSVERSELY ACROSS SAID PATH, A BURNER TIP DISPOSED ADJACENT SAID ONE WALL AND COAXIAL WITH SAID TUBE, AND MEANS FOR SUPPLYING A COMBUSTIBLE GAS TO AND BURNING 